Enhanced Performance in Cu(In,Ga)Se $_{\bf 2}$ Solar Cells Fabricated by the Two-Step Selenization Process With a Potassium Fluoride Postdeposition Treatment

Cu(In,Ga)Se 2 (CIGS) solar cells fabricated with two-step selenization processes commonly suffer from low open-circuit voltage ( $V_{{\bf oc}}$ ). We found that the $V_{{\bf oc}}$ of solar cells made from selenized Cu/Ga/In stacked metal precursors can be increased by employing a potassium fluoride (KF) postdeposition treatment (PDT). This study presents a comparison of films and resulting devices with and without the KF PDT. By including the KF PDT, an 18.6%-efficient CIGS device with a $V_{{\bf oc}}$ of 0.709 V was fabricated using a two-step selenization process.